Below is the British solution to a .22LR caliber personal defense weapon - the L66A1:
The British Army ordered 3000 of them in the mid 1970s for use by the Ulster Defense Regiment, an infantry regiment operating in Northern Ireland, for off duty carry.
The theory is that they wanted a non British military weapon in a non military caliber, presumably in the event a British soldier was caught with one it could pass as a personally owned weapon, and some folks suggest that the small caliber ensured no British soldier was going to
start a fight with one.
They are Walther PP pistols in .22LR with West German military proof marks and originally had no British proof marks at all. This one was FTR'd after it returned to Britain where they were used for training. Most of them were retired in the 1980's with about 1500 of them being imported to the US in the mid 1990s.
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As noted above, .22LR is not a great choice just based on the inherent reliability of he cartridge. Over the years, I've had numerous failures to fire with .22LR, even with high quality ammo. I expect to have one every 200-300 rounds. In contrast I can count the centerfire rounds that have failed to fire over 38 years of reloading and about 40 years of centerfire shooting on one hand, and I shoot a fair bit - a couple hundred rounds a week on average.
The Walther PP in .22LR has a 10 round magazine, but it won't feed the first two rounds reliably, so it is realistically an 8 round pistol - just like the 7.65mm Browning/.32 ACP Walther PP. In that regard I never understood why the British didn't just issue them stock Walther PP pistols in 7.65mm Browning, other than the possibility that they really didn't want their troops starting anything with them.
The Walther PP in .22 LR is also very particular about ammunition in terms of the momentum needed to cycle the slide. It needs high velocity ammo with 40 grain bullet to work reliably.
But with those caveats, mine has been extremely reliable mechanically. The only failures have been ammo related with 3 or 4 rounds every 500 rounds or so that either fail to fire, or lack enough power to fully cycle the slide.
Mine is very accurate, easily grouping around 2" at 25 yards and it's great fun to shoot and slightly lighter than a .32 ACP or .380 ACP PP, given the slightly thinner/lighter slide.
If you want to go small, I suggest consider a PP, PPK/S or PPK in .32 ACP. They are sweethearts to shoot, the cartridge is much more reliable, and it is much more effective than the .22LR.